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991.
Yuan L Zhang D Jemal M Aubry AF 《Rapid communications in mass spectrometry : RCM》2012,26(12):1465-1474
992.
Mohammed M. Babatin 《International Journal of Computational Fluid Dynamics》2013,27(10):723-735
In this article, we develop an adaptive scheme for solving systems of hyperbolic conservation laws. In this scheme nonlinear shock and linear contact waves will be treated differently. The proposed scheme uses the Kurganov central-upwind scheme. Fourth-order non-oscillatory reconstruction is employed near shock only while the unlimited fifth-order reconstruction is used for smooth regions and linear contact waves. To distinguish between the smooth parts and discontinuities, we use an efficient adaptive multi-resolution technique. The advantages of the scheme are high resolution and computationally efficient since limiters are used only for shocks. Numerical experiments with one- and two-dimensional problems are presented which show the robustness of the proposed scheme. 相似文献
993.
Raman Scattering at Resonant or Near-Resonant Conditions: A Generalized Short-Time Approximation 下载免费PDF全文
Abdelsalam Mohammed Yu-Ping Sun Quan Miao Hans ?gren Faris Gel mukhanov 《化学物理学报(中文版)》2012,25(1):31-47
We investigate the dynamics of resonant Raman scattering in the course of the frequency de-tuning. The dephasing in the time domain makes the scattering fast when the photon energy is tuned from the absorption resonance. This makes frequency detuning to act as a cam-era shutter with a regulated scattering duration and provides a practical tool of controlling the scattering time in ordinary stationary measurements. The theory is applied to resonant Raman spectra of a couple of few-mode model systems and to trans-1,3,5-hexatriene and guanine-cytosine (G-C) Watson-Crick base pairs (DNA) molecules. Besides some particular physical effects, the regime of fast scattering leads to a simplification of the spectrum as well as to the scattering theory itself. Strong overtones appear in the Raman spectra when the photon frequency is tuned in the resonant region, while in the mode of fast scattering, the overtones are gradually quenched when the photon frequency is tuned more than one vibra-tional quantum below the first absorption resonance. The detuning from the resonant region thus leads to a strong purification of the Raman spectrum from the contamination by higher overtones and soft modes and purifies the spectrum also in terms of avoidance of dissociationand interfering fluorescence decay of the resonant state. This makes frequency detuning a very useful practical tool in the analysis of the resonant Raman spectra of complex systems and considerably improves the prospects for using the Raman effect for detection of foreign substances at ultra-low concentrations. 相似文献
994.
Hongxia Wang Y. Sh. Mohammed Xiaobo Du Kai Li Hanmin Jin 《Journal of magnetism and magnetic materials》2009,321(19):3114-3119
The electronic structure and ferromagnetic stability of Co-doped SnO2 are studied using the first-principle density functional method within the generalized gradient approximation (GGA) and GGA+U schemes. The addition of effective UCo transforms the ground state of Co-doped SnO2 to insulating from half-metallic and the coupling between the nearest neighbor Co spins to weak antimagnetic from strong ferromagnetic. GGA+UCo calculations show that the pure substitutional Co defects in SnO2 cannot induce the ferromagnetism. Oxygen vacancies tend to locate near Co atoms. Their presence increases the magnetic moment of Co and induces the ferromagnetic coupling between two Co spins with large Co-Co distance. The calculated density of state and spin density distribution calculated by GGA+UCo show that the long-range ferromagnetic coupling between two Co spins is mediated by spin-split impurity band induced by oxygen vacancies. More charge transfer from impurity to Co-3d states and larger spin split of Co-3d and impurity states induced by the addition of UCo enhance the ferromagnetic stability of the system with oxygen vacancies. By applying a Coulomb UO on O 2 s orbital, the band gap is corrected for all calculations and the conclusions derived from GGA+UCo calculations are not changed by the correction of band gap. 相似文献
995.
We perform a holographic renormalization of the supergravity action and compute the stress tensor of the dual gauge theory incorporating the logarithmic running of the gauge coupling. From the stress tensor we obtain the shear viscosity and the entropy of the medium at temperature T, and investigate the ratio η/s. 相似文献
996.
Rachid Essehli Brahim El Bali Aziz Alaoui Tahiri Mohammed Lachkar Bouchaib Manoun Michal Duek Karla Fejfarova 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(12):i120-i124
The crystal structures of three isotypic orthorhombic dihydrogendiphosphates, namely dipotassium copper(II)/nickel(II)/zinc(II) bis(dihydrogendiphosphate) dihydrate, K2M(H2P2O7)2·2H2O (M = Cu, Ni and Zn), have been refined from single‐crystal data. The M2+ and K+ cations are located at sites of m symmetry, and the P atoms occupy general positions. These compounds also exist in triclinic forms with very similar structural features. The structures of both forms are compared, as well as the geometry of the MO6 octahedron, which is considerably elongated towards the water molecules for M = Ni and Cu. Such elongation has not been observed among the other representatives of the family. A Raman study of the whole series K2M(H2P2O7)2·2H2O (M = Mn, Co, Ni, Cu, Zn and Mg) is reported. 相似文献
997.
Abdelwareth A. O. Sarhan Mohammed S. Ibrahim Mostafa M. Kamal Kaiko Mitobe Taeko Izumi 《Monatshefte für Chemie / Chemical Monthly》2009,140(3):315-323
Abstract New ferrocenyl ketones were obtained as precursors of novel π-conjugated ferrocene-dithiafulvalene (Fc-DTF) and π-extended-ferrocenedithia-fulvalenes
(π-exFc-DTF) as electron-donor conducting materials from ferrocene by a direct aroylation process using the Friedel–Crafts
reaction. Novel Fc-DTF conjugates were synthesized using the Wittig–Horner reaction and their structures were determined.
The redox behavior of the ferrocenyl carbonyl compounds Fc-DTF and Fc-π-exDTF was investigated in comparison to the parent
ferrocene by means of cyclic voltammetry. A one-electron redox behavior was observed for carbonylferrocenes as one wave potential,
while a two-electron process was observed as two oxidation waves for the conjugates. Introduction of electron-withdrawing
groups led to increasing E
pa values and decreasing ΔE
p
values. The UV–Vis spectra of some compounds were studied in comparison with ferrocene. The absorption spectra showed a red-shift
with a slight increase in the absorption intensities.
Graphical abstract
相似文献
998.
Mohammed Krouit 《European Polymer Journal》2009,45(4):1250-3539
Two series of porphyrinic cellulose laurate esters plastic films, where the photosensitizers are covalently linked to the cellulosic polymer have been synthesised by using a “one-pot, two-step” esterification reaction. The photosensitizers were first covalently bounded to the cellulosic polymer using either 4- or 11-carbon spacer arms. The porphyrinic plastic films were then obtained by a second esterification with lauric acid. The reaction was studied according to reaction time, temperature, lauric acid amount, pyridine playing the role proton trapping base. Para-toluenesulfonylchloride has been proved to be a powerful activating agent for this reaction. The drawback of the steric hindrance of the porphyrinic macrocycle towards cellulosic hydroxyl groups has been overcome by increasing the number of carbon of spacer arms from 4- to 11-carbons. The photobactericidal activity of these materials was evaluated against Gram positive and Gram negative strains bacteria. First results show that these new plastic films display photobactericidal activity for porphyrin grafting percentage higher than 0.16, whereas the non-porphyrinic control allowed full growth of bacteria. These materials could be an alternative in order to overcome the growing bacterial multiresistance to classical antibiotics. 相似文献
999.
Reduction kinetics of thionine (Th) with D-galactose (RH) was observed on a UV/Visible 1601 Shimadzu spectrophotometer at λmax 599 nm. The results showed that the initially slow reduction kinetics got enhanced and proceeded to completion within a few minutes. A pseudo first order kinetics was observed when influence of different parameters like concentration of dye and reductant, ionic strength and temperature was investigated. A significant shift in wave length from 599 to 517 nm was observed at alkaline pH whereas addition of a small amount of acid caused a shift in equilibrium. This resulted in the generation of oxidized form of thionine which was pragmatic in the presence of atmospheric oxygen. Change in ionic strength at elevated temperature lied to decrease in the rate constant. Thermodynamics activation parameters like Ea reflects a high amount of energy required for reduction of Th with RH whereas entropy of activation (∆S!) and free energy of activation (∆G!) show the highly solvated states of transient complex which was less disorderly arranged than the oxidized form of dye. A mechanism consistent with above findings has been discussed in the relevant section of paper. 相似文献
1000.
Jos M.F. Ten Berge Alwin Stegeman Mohammed Bennani Dosse 《Linear algebra and its applications》2009,430(2-3):818-829
The Candecomp/Parafac algorithm approximates a set of matrices by products of the form , with diagonal, . Carroll and Chang have conjectured that, when the matrices are symmetric, the resulting and will be column wise proportional. For cases of perfect fit, Ten Berge et al. have shown that the conjecture holds true in a variety of cases, but may fail when there is no unique solution. In such cases, obtaining proportionality by changing (part of) the solution seems possible. The present paper extends and further clarifies their results. In particular, where Ten Berge et al. solved all cases, now all cases, and also the cases for , and 9 are clarified. In a number of cases, and necessarily have column wise proportionality when Candecomp/Parafac is run to convergence. In other cases, proportionality can be obtained by using specific methods. No cases were found that seem to resist proportionality. 相似文献